This application claims priority to an application entitled xe2x80x9cFlow Control Method in Packet Switched Networkxe2x80x9d filed earlier in the Korean Industrial Property Office on Oct. 12, 1998 and assigned Ser. No. 98-42606, and an application entitled xe2x80x9cFlow Control Method in Packet Switched Networkxe2x80x9d filed earlier in the Korean Industrial Property Office on Oct. 12, 1998 and assigned Ser. No. 98-42607, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to a packet switched network, and in particular, to a flow control method in a LAN (Local Area Network) that can minimize the loss of packet data over the LAN such as Ethernet and allow a bandwidth to be equally shared among the input ports of the LAN device.
2. Description of the Related Art
Congestion condition associated with Ethernet is generally overcome by applying a back pressure or transferring a pause frame in the Ethernet system. The back-pressure is applied when an Ethernet switch is in a half duplex mode, and the pause frame transfer scheme is applied when an Ethernet switch is in a full duplex mode. The pause frame is one form of MAC (Media Access Control) control frames which is defined under the IEEE 802.3x standard. These two schemes control the flow of information and prevent the Ethernet switches from sending packet information temporally to a specific Ethernet switch when the buffer capacity of the specific Ethernet switch reaches its limit or when congestion occurs.
The back-pressure scheme transmits a jamming signal used in the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) method to remedy the congestion condition. Upon sensing the congestion condition from a specific Ethernet switch (downstream), a jamming signal is trasnsmitted to the other Ethernet switches (upstream) within the same segment to stop the packet transmission for a predetermined random back-off period until the congestion condition is cleared.
On the other hand, the pause frame scheme transmits a pause frame, which is one form of MAC control frames defined under the IEEE 802.3x standard, to remedy the congestion condition. If an Ethernet switch (downstream) suffers a congestion, a specific pause frame is transmitted to the other Ethernet switches (upstream) in the same segment so that the other Ethernet switches stop transmitting the packet data for the duration of a pause time period as specified in the pause frame. After the congestion condition is cleared, the transmission of packet data is resumed.
As described in the above, a jamming signal or a pause frame is introduced to compensate for the congestion condition. If the Ethernet switch (downstream, hereinafter referred as xe2x80x9cdownstream Ethernet switchxe2x80x9d) suffers congestion, the jamming signal and the pause frame are transmitted to the plurality of Ethernet switches (upstream, hereinafter referred as xe2x80x9cupstream Ethernet switchesxe2x80x9d) through the input ports connected to each upstream Ethernet switch. However, the conventional flow control method is likely to stop the packet transmission for all the upstream Ethernet switches even when the packet transmission from the upstream Ethernet switch is not the source of congestion.
It is, therefore, one of the objects in accordance with the present invention is to provide a method for equally sharing a buffer capacity among the input ports of Ethernet switches.
It is another object of the present invention to provide a method for minimizing the packet loss due to a congestion in the Ethernet switch.
It is a further object of the present invention to provide a method for increasing a packet processing rate over the entire network.
To achieve the above described objects, a method for controlling the flow of traffic in an Ethernet switch, namely, a downstream device using a full duplex mode in the packet switched network of the type having a plurality of input ports coupled to a plurality of upstream Ethernet switches, and a common memory for storing the packet data received from each input port and for transmitting the packet data read from the common memory to the destination upstream Ethernet switch. In such flow control method, the buffer state of the common memory is first determined. If the buffer state is full, a pause frame having a predetermined pause time is transmitted to the plurality of upstream Ethernet switches and an expected pause time of the upstream devices is initiated. Thereafter, if the expected pause time expires, the buffer state of the common memory is determined again. If the buffer state is still full, the pause frame having a predetermined pause time is re-transmitted to the plurality of upstream Ethernet switches and the expected pause time of the upstream devices is re-initiated.